Paint spraying method

ABSTRACT

A method and apparatus for spraying paint and similar coatings. In one form the paint is sprayed at low pressure from a flat fan nozzle. A flat fan of air impinges upon the fan of paint at an angle of from 30*-70*. The air atomizes the paint to form a soft spray with low forward velocity. In another form of the method, two fans of paint are projected toward one another at an angle and an air fan is directed along the bisector toward the zone of intersection. The air fan atomizes both streams of paint. An electrode can be placed in the air stream to ionize the air stream which in turn charges the paint particles. The width of the paint spray pattern is varied by varying the included angle of the air fan. A spray gun is disclosed having two tubular paint nozzles for projecting two fan-shaped fans of paint. An air nozzle is mounted between the paint nozzles for projecting a fan of air against the paint fans to atomize the paint. The air nozzle is adjustable to provide air fans of different angles for varying the width of the paint spray pattern. An electrode is disposed in the air nozzle for ionizing the air stream. This electrode is energized through a resistor and flexible cable. The cable is spring-urged toward the resistor so that when the resistor is removed, the cable shifts causing a safety switch to open deenergizing the gun. When a nozzle mounting member is removed, the cable and surrounding tube are shifted forwardly to automatically close a valve to seal off the air and electrical conduits. Removable caps are provided on the ends of the tubular paint nozzles for facilitating cleaning of the nozzles.

United States Patent [1 1 Nord et al.

[451 July 24, 1973 PAINT SPRAYING METHOD [75] Inventors: Eric T. Nord,Oberlin; Samuel R.

Roseu, Lorain; Don R. Scarbrough, Elyria; Burton J. Vilagi, Amherst, allof Ohio; Peter W. Ruustadler, Jr., Hanover, NJ.

[73] Assignee: Nordson Corporation, Amherst,

Ohio

[22] Filed: Sept. 2, 1971 [2]] Appl. No.: 177,432

Related US. Application Data [62] Division of Ser. No. 23,227, March 27,1970, Pat. No.

[52] US. Cl. 239/8 [51] Int. Cl. A01u 17/02, A620 1/12 [58] Field ofSearch 239/422, 8, 3, 10, 239/292, 300

[56] References Cited UNITED STATES PATENTS 1,881,345 10/1932 Beatty etal 239/422 3,606,154 9/1971 Tufts 239/422 Primary Examiner Lloyd King 7AttorneyWood, Brinkman, Jr. et al.

[5 7 ABSTRACT A method and apparatus for spraying paint and similarcoatings. In one form the paint is sprayed at low pressure from a flatfan nozzle. A flat fan of air impinges upon the fan of paint at an angleof from 30-70. The air atomizes the paint to form a soft spray with lowforward velocity. In another form of the method, two fans of paint areprojected toward one another at an angle and an air fan is directedalong the bisector toward the zone of intersection. The air fan atomizesboth streams of paint. An electrode can be placed in the air stream toionize the air stream which in turn charges the paint particles. Thewidth of the paint spray pattern is varied by varying the included angleof the air fan.

A spray gun is disclosed having two tubular paint nozzles for projectingtwo fan-shaped fans of paint. An air nozzle is mounted between the paintnozzles for projecting a fan of air against the paint fans to atomizethe paint. The air nozzle is adjustable to provide air fans of differentangles for varying the width of the paint spray pattern. An electrode isdisposed in the air nozzle for ionizing the air stream. This electrodeis energized through a resistor and flexible cable. The cable isspring-urged toward the resistor so that when the resistor is removed,the cable shifts causing a safety switch to open deenergizing the gun.When a nozzle mounting member is removed, the cable and surrounding tubeare shifted forwardly to automatically close a valve to seal off the airand electrical conduits. Removable caps are provided on the ends of theI tubular paint nozzles for facilitating cleaning of the nozzles.

37 Claims, 19 Drawing Figures PATENTED JULNW 3. 747. 852

' SHEEI 2 [IF 7 PATENTED' JUL24|975 3. 747, 852

SHEET 3 [IF 7 PArEmwJuLzmza SHEEI 5 IF 1 PAINT SPRAYING METHOD Thisapplication is a division of parent patent application Ser. No. 23,227,filed Mar. 27, 1970, now U.S. Pat. No. 3,635,400, issued Jan. 18, 1972in the names of Eric T. Nord et al.

BACKGROUND OF THE INVENTION This invention relates to methods andapparatus of spraying paints, lacquers and similar coating materials andis particularly directed to a novel method and apparatus for effectingair atomization of the paint and for electrostatically charging thepaint if desired so that the electrostatic field forces can be utilizedto increase the effectiveness of paint deposition.

In the past there have evolved two distinct types of paint sprayingequipment. The first type can be characterized as airless sprayingequipment. In an airless type of spraying apparatus,a paint stream isforced through an orifice under a relatively high pressure, for example,a pressure of the order of 300-l,000 pounds. As the paint is propelledthrough the small orifice it is broken up, or atomized, into very finedroplets. The paint spray formed from the gun moves at a relatively lowvelocity toward the article to be painted. In many cases the paintspraying operation is carried out in the presence of a high voltageelectrostatic field in which.

the work to be coated is kept at, or close to, ground potential whilethe atomized paint particles are charged to a relatively high potential.These particles are then urged toward the work by the forces of theelectrostatic field.

This type of system has the recognized advantage of providing a veryhigh deposition efficiency, i.e. a large portion of the paint sprayemitted from the gun is effectively deposited on the article to becoated. On the other hand, in some installations the airless spray-typeapparatus has certain inherent shortcomings. One such objectionablecharacteristic is that the system requires a paint supply systemoperated at a relatively high pressure. As a result, it is not feasibleto disconnect a gun from one high pressure paint line and quicklyconnect it to another high pressure paint line when, for example, it isdesired to change the color of coating being sprayed.

The second general type of spray equipment does not require a highpressure paint source. This second type of spray system, which is knownas air spray equipment, relies upon a stream of air to break up thepaint into particle size suitable for spraying. In conventional airspray equipment, the paint is extruded from a nozzle in a generallyrod-like form and is subjected to a high pressure blast of air. In atypical air spray installation, the air pressure at the gun is under apressure of approximately the order of 75 pounds per square inch. Theair is used in large quantities; for example, it is common practice toutilize an air flow of 14 or 15 standard cubic feet of air per minute tocarry out atomiza' tion.

Air spray systems of this type do present certain advantages in thatthey can be utilized to atomize particularly difficult types of paintand can more readily be provided with quick disconnect couplings to thepaint line since the paint line is maintained at a relatively lowpressure of, for example, 50 psi. At the same time, however, prior artpaint spray guns are subject to several disadvantages.

In the first place, the large quantity of high velocity air used toatomize the paint together with the air flow it induces causes asubstantial portion of the paint spray to be carried past the workpieceand wasted even when an electrostatic charge is applied to the paint.Moreover, the rapidly moving air has a high kinetic energy which causesit to bounce back or rebound from the surface being coated carrying withit entrained paint particles. Consequently, an appreciable portion ofthe paint which is directed toward the workpiece is wasted due torebound.

Another inherent disadvantage of conventional air spray equipment is theproblem of ventilation. Specifically, because of the high volume of airemitted by each spray gun, and in many installations there are severalguns operating simultaneously, a ventilation system must be providedhaving a high capacity for capture of paint particles entrained in thelarge mass of high-speed air, for example, capture velocities of feetper minute.

Also, because of paint entrained in the large amount of over-spray andrebound, water curtains or other types of filters must be provided forpreventing sizable quantities of paint from escaping and polluting theatmosphere.

SUMMARY OF THE INVENTION The principal object of the present inventionis to provide a novel method and apparatus for spraying paint in whichrelatively small quantities of air at a relatively low pressure areutilized to atomize the paint in a very effective manner so that theresultant paint spray is a soft, finely divided spray not unlike thatwhich could heretofore be produced only by an airless gun.

At the same time, the present method and apparatus are effective toretain the advantages inherent in any air-type of spray gun, i.e. theability to atomize various difficult types of coating material and thefacile interconnectability to various paint lines so that the spary guncan be converted quickly from spraying one color or type of coating toanother.

More particularly, the present invention is predicated in part upon theconcept of spraying paint by emitting a thin, flat fan-shaped stream ofpaint from one nozzle and a fan-shaped stream of air from a secondnozzle. The paint fan in most cases is initially in the form of acontinuous sheet. However, the fan can be in the form of a thin,substantially planar discontinuous spray; for example, one which isalready partially atomized. The fan-shaped stream of paint and airimpinge upon one another at a substantial angle of from approximately30-70. The air thus exerts an optimum shearing force upon the paint fanand breaks the paint down into small particles of a low mean particlesize with substantially no particles of an objectionably large size.

This invention is further predicated in part upon the empiricaldiscovery and determination of various physical relatioships and valuesof certain parameters which make it possible to obtain an atomizationsuitable for fine finishing purposes utilizing as one starting componenta low pressure fan of paint. A flat stream of paint from any presentlyknown form of fan nozzle operated at low pressure is inherently in avery difficult form to atomize into small particles with the uniformityrequired for producing satisfactory painted surfaces.

The difficulties involved are due to the fact that the paint stream isnot a uniformly thin flat sheet. Rather,

the sheet in cross-section is somewhat like a dumbbell with a thincenter web and two enlarged portions, one at each edge. These enlargedportions are in fact longitudinal beads or streamers. These twostreamers are several times the thickness of the central web portion andtend to remain integral and resist atomization even when the rest of thesheet is broken up into particles. It will readily be appreciated thatno matter how finely most of the paint is atomized, if the streamers arenot broken up into particles of generally the same fineness, the qualityof the applied coating will suffer and may well become totallyunacceptable. The present paint spray method is effective to causeeffective break-up of all parts of the paint stream, including thestreamers, into small particles while using only a relatively smallquantity of air.

In accordance with the present invention, the air stream is projectedunder a relatively low pressure, for example, of the order of 9 to 45pounds per square inch at the gun, while the paint is sprayed under alow pressure of, for example from 30-80 pounds per square inch. Thismethod of atomization is so effective that the quantity of air requiredto deposit a relatively large quantity of paint, for example, 22-25fluid ounces per minute of a typical baking enamel, is approximately 7-8standard cubic feet per minute. As a result of this small volume of lowpressure air and the fine atomization of the paint, the resultant sprayis in the nature of a soft spray, or slowly moving fog, having a lowforward velocity.

One of the principal advantages of this method of spraying is that itresults in a substantially higher deposition efficiency thanconventional air spraying methods. There is substantially less paintwaste due to overspray and rebound which is minimized or practicallyeliminated.

Another advantage of the present spray method is that the relativelysmall quantity of air involved and the smaller quantity of paintentrapped in the exhausted air greatly simplifies the problem ofventilation and prevention of atmospheric contamination.

Another object of the present invention is to provide a novel method forreadily changing the width of the paint spray pattern. This aspect ofthe present invention is predicated upon our determination that thewidth of the paint spray can be controlled by changing the includedangle of the air fan without in any way changing the paint fan.

in accordance with the present invention, the air fan is selectivelyemitted from one of a series of nozzle openings constructed so that thenozzle openings not only simultaneously produce air fans of differentincluded angles, but also produce air fans which behave much as thoughthey are emitted from a point pressure source, the distance from thenozzle opening of which is varied in an inverse relationship to theangular size of the nozzle opening. By virtue of this relationship, theheight of the air fan along its line of impingement with the paintstream is maintained substantially constant so that all portions of thepaint stream are effectively atomized with a minimum air usage.

in addition to the method concepts disclosed above, the presentinvention also comprehends a preferred spray painting method utilizingin part the method described. More particularly, in the preferred methoda fan of air is in effect enveloped between two fans of paint. The fansof paint are directed toward each other with the air fan bisecting theangle so that it impinges upon both paint streams in substantially thesame zone. This method results in an even better atomization than thesingle spray method, apparently due to the fact that in order to escape,a major portion of the air must pass through one or the other paintstreams or through the paint particles being separated from the streams.Thus, the kinetic energy of the air is more effectively utilized toshear the paint and cause its break up into particles of a small meanparticle size.

The present two-paint stream method of spraying is also particularlyadvantageous when employed in conjunction with the present novel methodof electrostatic charging. More particularly, in accordance with thepresent charging method, the paint is not charged directly or by anelectrode in close proximity to the paint stream. Rather, it is ourconcept to ionize the air fan prior to its impingement upon the paintstreams by passing the air fan through a corona discharge surrounding anelectrode at a high potential. As explained above, the air fan thenimpinges upon the paint streams and causes the atomization of the paintstreams.

The ions present in this air stream have a high mobility and aresubjected to the forces of the surrounding electrostatic field.Specifically, these ions, which are charged and exist in a field of highpotential, move toward the paint streams and fog of paint dropletsexisting in regions of a lower potential. The ions attach themselves tothe paint particles which are of substantially lower mobility. Thesecharged paint particles are propelled forward by the air stream andunder the additional influence of the electrostatic field forces arebrought into contact with the surface to be coated which is normallymaintained at ground potential.

We have determined that the two-paint stream method results insubstantially more effective charging of paint particles than theone-spray method and believe that this is due to the fact that the ionsare to a large degree surrounded by the paint streams and particles anddo not have a free path to one side of the paint as is the case whenonly a single paint spray is utilized.

The present method of charging paint is not only advantageousbecause ofits high efficiency, but is further advantageous because the entirepaint supply system, including the tube supplying paint to the gun, thepaint pump and the paint reservoir, or tank, remain at or near groundpotential.

In contrast, in prior art electrostatic spraying systems, particularlywhen a conductive paint or coating, such as one of themetallic-containing finishes utilized in the automobile industry, isused, the entire paint system became charged to the same order ofpotential as the electrode, e.g. 75,000 volts. This necessitated carefulinsulation of the entire paint system including the paint reservoir. Inthe event of insulation failure, for example in the paint supply tube,the high potential present could, and not infrequently did, result infires, electrical shock hazards, and other operational difficulties. Allof these problems are completely eliminated by the present chargingmethod in which no charge is applied directly to the paint either by anelectrode in contact with the paint or by an electrode in closepromximity to the paint stream.

In addition to the method aspects of the present invention, theinvention is directed to the provision of a novel spray gun for carryingout the method. More particularly, the present spray gun includes ahandle, a forwardly extending barrl and a nozzl assmbly mountd at theforward nd of the barrl.

The nozzle assembly comprises two tubular paint nozzles effective todirect thin flat fan-shaped paint sheets toward the axis of the gun, andan air nozzle mounted between the paint nozzles and effective to directa flat fan-shaped stream of air along the axis of the gun toward thezone of intersection of the two paint fans. In accordance with thepresent invention the air nozzle and paint nozzles are located so thatthe distance of the air nozzle from the zone of air-paint impingement isonly a fraction of the distance of the paint nozzles from the zone ofair-paint impingement. 'As a result, the velocity of the air issuingfrom the nozzle is attenuated only minimally prior to its impingementwith the paint fans. Each of the paint fans and air fan meet at asubstantial angle of the order of 30 to 70. As a result, the air fanexerts an optimum shearing force on the paint fans and breaks up bothfans simultaneously into a spray of particles of small mean particlesize free from inordinately large particles.

One of the advantages of the present gun is that it is quite compact andmaneuverable. Despite the fact that the gun utilizes three separatenozzles it is as small and easy to handle as previous spray guns of theair or air less type.

It is another objective of the present invention to provide a spray gunincorporating paint charging means of a substantially increasedefficiency. In fact, the present electrostatic charging system is soefficient that when operated at 50,000 volts or even less, it providesthe same deposition efficiency as is attained using a conventionalelectrostatic charging mechanism operating at a potential of 75,000volts.

More particularly, in accordance with the present invention the gunincludes an electrode mounted within the center air nozzle in alignmentwith the nozzle discharge opening. This electrode is effective toestablish a corona through which the air passes prior to its dischargefrom the nozzle. As the air passes through the corona the gas moleculesare ionized and dust particles charged. These charged particles moveunder the electrostatic field forces toward the paint which is at a lowpotential and are subsequently deposited on the low mobility paintparticles.

As indicated above, one of the principal advantages of this invention isthat the paint stream itself does not become charged so that there is atmost a negligible charge build-up in any portion of the paint supplysystem.

Another objective of the present invention is to provide a chargingcircuit which is substantially safer to use than the prior art. Moreparticularly, in many conventional prior art charging systems thecharging electrode projects forwardly from the end of the spray gun.This high potential electrode is thus in an exposed position in which itcan be touched accidentally by a workman or can be shorted by accidentalcontact with a grounded conductor. In contrast, the electrode of thepresent invention is buried within the air nozzle where it iseffectively shielded from any contact with either the person using thegun or a grounded surface.

The present gun also embodies a second important safety feature whichautomatically prevents the application of a high potential to the gun inthe event that the current-limiting safety resistor is left out. Moreparticularly, it is common practice to provide a resistor in series withthe electrode and the cable connecting the power pack to the gun. When aspray gun is overhauled, the resistor is often removed and at times aworkman may neglect to replace it when reassembling the gun. When such aresistor is omitted the full potential from the power pack can becapacitively discharged across the void and applied to the gunelectrode. In such a case, if a gun is brought too close to a groundedarticle, a spark may occur which might cause an ignition of the paintmaterial or cause a painful electrical shock to the operator.

In accordance with the present invention, this is prevented by a novelsafety switch arrangement in which the main power is automatically cutoff whenever the resistor is removed from the gun.

Another objective of the present invention is to provide a constructionin which the air and electrical conduits are automatically sealed offwhen the gun is disassembled by removing the nozzle assembly. Inaccordance with the present invention, this is accomplished by providinga valve seat at the forward end of the air and electrical conduit in thegun barrel and by providing a shiftable sleeve having a valve-closingplug at its forward end. When the gun is disassembled, this sleeve isspring-urged to the valve closing position to seal off the entrance tothe air and electrical conduit. In so moving, it alao cuts off the powersupply.

A still further objective of the present invention is to provide a novelform of air nozzle for selectively vary ing the air spray to change thesize of the paint spray pattern.

In a preferred form of nozzle, the angle of air spray is changed byselectively emitting the air through one of a series of openings in anozzle plug. The plug is provided with internal arcuate surfaces ofdifferent radii adjacent to each nozzle opening. We have made theempirical discovery and determination that air projected from such anozzle appears to have somewhat the same properties as air emitted froma point source which is displaced from the nozzle opening a distancecorrelated with the radius of the internal nozzle surface.

To obtain a fan spray having a smaller included an gle, the plug isshifted to present an opening in which the radius of this internalsurface is greater so that a smaller segment of its periphery is cutaway. This results in an air fan of smaller included angle and at thesame time results in a shifting of the point source away from the nozzleopening. The net effect, as far as matching the width of the paint fans,is thus similar to shifting the nozzle away from the paint film. As aresult, although its angle is smaller, the height of the air fan alongthe line of impingement of the paint film remains unchanged.Consequently, neither a large portion of the air stream is wasted bypassingoutside the confines of the paint film, nor are portions of thefilm improperly atomized due to the fact that they are not impinged uponby the air stream. At the same time the distance the air has to travelto reach the zone of impingement is minimized.

These and other objects and advantages of our invention will be morereadily apparent from a consideration of the following detaileddescription of the drawings illustrating the principles involved in thepresent method of paint spraying and a preferred form of apparatus forcarrying out the method.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic view of a paintspray system embodying the present invention.

FIG. 2 is a semidiagrammatic elevational view of a paint spray issuingunder relatively low pressure from a fan nozzle.

FIG. 3 is a cross-sectional view of the paint spray taken along line 3-3of FIG. 2.

FIG. 3A is a diagrammatic view plotting the preferred distribution ofmass flow rate from an air nozzle used to atomize a paint spray film.

FIG. 4 is an enlarged top plan view of a portion of the paint spray filmshown in FIG. 2 illustrating the manner in which the paint spray filmdecreases in thickness as it travels away from the nozzle.

FIG. 5 is a diagrammatic view showing the cooperative relationshipbetween a paint spray nozzle and an air spray nozzle in carrying out thepresent paint spray method.

FIG. 6 is a semi-diagrammatic view taken along line 6-6 of FIG. 5.

FIG. 7 is a diagrammatic view showing the relationship of two paintnozzles and an air nozzle to carry out a preferred method of paintspraying in accordance with the present invention.

FIG. 8 is a view taken along line 8-8 of FIG. 7.

FIG. 9 is a longitudinal sectional view of a preferred form of spray gunconstructed in accordance with the present invention.

FIG. 10 is an enlarged cross-sectional view taken along line 10-10 ofFIG. 9 and with portions rotated 90 for purposes of clarity.

FIG. 11 is a view taken along line 111l of FIG. 10.

FIG. 11A is a front elevational view of the air nozzle plug.

FIG. 12 is a cross-sectional view taken along line l2-I2 of FIG. 10.

FIG. 13 is a cross-sectional view taken along line l3l3 of FIG. 10.

FIG. 14 is a cross-sectional view taken along line l4-l4 of FIG. 10.

FIG. 15 is a semi-diagrammatic view showing the relationship of the airnozzle and paint film to a target.

FIG. 16 is a diagrammatic view similar to FIG. 15 showing the manner inwhich the air nozzle opening and spacing from the paint film are variedto decrease the width of paint spray.

FIG. 17 is a schematic circuit diagram of the safety circuit.

SYSTEM FIG. I shows a paint spray system 10 for spraying paints andother coatings in accordance with this invention. As is well recognizedin the art, coating systems of the general type shown are utilized toapply coatings to many different types of products, such as automobileparts, furniture, containers, and the like. The coating materialsutilized include not only paints, but also enamels, lacquers, stains,varnishs, emulsions, waxes, adhesives, and the like. In the followingdscription the word paint" will b used in a very generic sense toencompass all of these various types of coating materials.

In almost all instances, it is desirable that the paint or other finishbe applied in a smooth, even coating with the particles deposited on theworkpiece being of a small and relatively uniform size. Paint systemsfor carrying out the present process include a spray gun 11 which issupplied with paint by means of a pump 12 which feeds paint underpressure to the gun from a paint supply tank 13 through a paint tube 14.(Alternatively pump 12 can be eliminated and tank 13 pressurized). Thegun is also supplied with air under pressure from a conventionalcompressor or other air pressure source. The air is applied to the gunthrough an air tube 15.

As is well known in the art, when spraying some types of products, forexample, the interiors of deep tubular structures, it is desirable tooperate the system as a straight air spray system without applying anyelectrostatic field. However, in spraying other types of articles, it isdesirable to charge the paint particles so that the deposition of theparticles is aided by the presence of a high electrostatic field. Insuch instances, the article being sprayed is normally maintained atground potential so that the electrostatically charged paint particlesmove toward the article under the influence of the electrostatic fieldforces and a high percentage of them are effectively deposited on thearticle to be painted.

The present system can be operated either as a straight air spray gun oras an electrostatic air spray gun. In the event that the gun 11 is to beoperated as an electrostatic unit, it is connected to a power pack, orsource of DC voltage, 16. The power pack is connected to the gun throughan electrical cable 17.

Gun 11 may either be a hand-held gun or can be an automatic gun mountedon a suitable support normally positioned adjacent to a conveyor line bymeans of which the articles to be sprayed are moved past the gun. Ineither case, and particularly in the case of handheld guns, it isdesirable that the gun itself be compact and maneuverable. With eitherform of gun the paint particles are atomized by a low pressure stream ofair and are porjected forwardly from the gun in a soft spray of fineparticles. A typical spray pattern of the present system travels onlyabout one-half of the travel of a conventional air spray gun operatedunder the same conditions.

PAINT SPRAYING METHOD In order to understand various ramifications ofthe present paint spraying process, it is desirable to consider thenature of a fan-shaped paint spray film as it is sprayed from a nozzleunder relatively low air pressure. The pattern of a typical paint film18 is illustrated in FIG. 2. The film is being emitted from a nozzle ofthe flat fan spray-type. Such nozzles are conventionally utilized inairless spray guns and one form is disclosed in Bede US. Pat. No.2,754,228. Another form of fan spray nozzle is disclosed in detailbelow. The paint film shown in FIG. 2 is being sprayed under arelatively low pressure, for example, a pressure of the order of 40-50psi as opposed to the normal pressure used in airless spray guns of theorder of 300-] ,000 psi.

As shown in FIGS. 2-4, the paint film is discharged from the orifice ina generally fan-shaped pattern with the upper and lower edges of thefilm diverging. The angle of divergence of these upper and lower edgesgradually decreases. The film is not uniform in cross section. Rather,for a short distance as it leaves the nozzle 20, the film includes acentral, relatively uniform web 21 and two edge enlargements orstreamers 22 and 23. These bead-like streamers run along the upper andlower edges of the fan and are substantially thicker than the centralweb portion 21.

When low hydraulic pressures are used, such a film of viscous coatingmaterial remains relatively stable for a distance of perhaps 1 inch toseveral inches after it leaves the nozzle. However, at the end of thisstable region the film begins to form transverse ripples, or waves, 24.As the sheet becomes more, more and more unstable, the waves 24eventually disintegrate into ligaments and droplets 25. However, thestreamers persist and strongly resist disintegration.

In addition to these characteristics, the thickness of the filmdecreases progressively as the film leaves the nozzle. This decrease infilm thickness is generally inversely proportional to the distance fromthe nozzle so that the most rapid diminution of sheet thickness occursin the first fraction of an inch (e.g. one-fourth inch) of sheet travelfrom the nozzle and from that point on the rate of diminution issubstantially smaller.

The broadest aspect of the present paint spraying method is illustratedin FIGS. and 6. Essentially, we have determined that very fine paintatomization characterized by low mean particle size and freedom fromrandom large particles can be obtained by spraying a fan-shaped film ofpaint 27 under relatively low pressure, for example, a pressure of theorder of 30-80 psi,

from a nozzle 28 and impinging this fan-shaped paint spray with afan-shaped stream of air 30 emitted under a very low pressure of theorder of 9-45 psi by an air nozzle 21 When the air stream impinges uponthe paint fan, it exerts a strong shearing force on the film andeffectively atomizes all portions of the paint stream, including thestreamers 32 and 33. The paint stream is deflected and continuesoutwardly as a soft spray pattern, or fog, 34 of suitably atomized paintparticles.

In accordance with the present method, the paint is struck by arelatively small volume of air at a relatively high velocity. We haveempirically determined that optimum atomization of particles for paintspraying is ob tained when the angle at between the paint spray film andthe air spray is made between approximately 30 and 70. The line ofimpingement 35 between the air stream and paint stream is spaced farenough from the nozzle so that the paint stream has undergone a greaterportion of the attenuation of its thickness. At the same time, the lineof impingement 35 against a stream of the type shown in FIG. 2 shouldoccur within the region in which the paint film is substantially planar,i.e. before the transverse waves 24 would commence in the absence of anair stream.

Next, the length L A of the path of travel from the air nozzle 31 to theline of impingement 35 should be only a fraction of the correspondinglength L of the paint film from the paint nozzle 28 to the line ofimpingement 35. We have empirically determined that the preferred rangeof ratio of L /Lp is from one-sixth to threefourths. In one preferredembodiment, the actual length of paint film L is approximatelythree-eighths to three-fourths inch, while the actual length of air filmL is approximately one-eighth to three-eighth inch. The air stream isslightly wider (from edge-to-edge) along the line of impingement 35 ofthe paint film than is the paint film. This facilitates breaking up andeffective atomization of the streamers 32 and 33 which is essential toobtaining a good quality paint spray.

To further improve the atomization of the streamers, the air sprayitself is made non-uniform with the air stream having higher mass flowrates adjacent its edges, in the areas of the stream which impinge uponstreamers 22 and 23. This is shown diagrammatically in FIG. 3A in whichthe mass flow rate of the air is shown as being substantially greater inthe areas 36 and 37 in which the air stream impinges upon the streamers22 and 23 than in the central area 38 of the air stream which impingesupon the thin web portion 21 of the paint film.

In practice, this non-uniform air stream can be obtained by emitting airfrom a thin slot which is not of rectangular configuration, but ratheris wider adjacent to the ends. In many cases, however, the use of such aspecially conflgurated nozzle is not necessary since we have found thatthe use of a flat fan nozzle made with a rectangular gash gives asufficiently heavy edged air flow to atomize the heavy edges of thepaint sheets.

In carrying out the present process, paint can be applied at a high ratewithout adversely affecting the highly effective atomization achieved.Moreover, this fine and uniform atomization'is achieved while utilizingonly a relatively low amount of air in relation to the quantity ofpaint. For example, on one typical operation an acrylic enamel having aviscosity of 22 seconds as measured by a Zahn No. 2 cup at roomtemperature was sprayed at a rate of 22 fluid ounces per minute. Thepaint pressure was approximately 40 psi and the air pressure was 20 psiat the gun. The air flow was at the rate of 8 standard cubic feet perminute so that the ratio of air-to-paint was 0.36 standard cubic feet ofair per fluid ounce of paint sprayed per minute. Conventional air sprayguns utilize an air-to-paint ratio approximately twice this large and anair pressure of approximately psi. Consequently, the total energy of theair utilized in the present process is only a small fraction of thatrequired in a conventional air gun. This same relatively low ratio ofair volume-to-paint is utilized in the present method through the entirerange of viscosities of coating materials which are normally appliedusing the present method.

For example, a very viscous vinyl coating having a viscosity of 40seconds as measured on a Zahn No. 2 cup at room temperature wasdeposited at the rate of 17.2 fluid ounces per minute. The paintpressure was 45 psi and the air pressure was 26 psi at the gun. Thevolume of air employed was 9.5 standard cubic feet per minute. Thus, theratio of air to ounces of paint was 0.55 standard cubic feet of air perminute per fluid ounce of paint per minute.

As another example, a stain having a very low viscosity of 16.5 secondsas measured on a Zahn No. 2 cup at room temperature was applied at arate of 24 fluid ounces per minute. Again, the paint pressure was 45 psiand the air pressure was 9 psi at the gun. The amount of air employed toatomize this stain was 4.5 standard cubic feet per minute orapproximately 0.18 standard cubic feet of air per minute per fluid ouncepaint per minute. In each of the above two examples, the air utilized bya conventional spray gun was approximately twice the amount utilized inthe present spray gun.

An even more advantageous version of the present paint spraying processis disclosed in FIGS. 7 and 8. In this preferred method of sprayingpaint, two substantially identical fan-shaped sprays of paint 40 and 41are emitted from fan spray nozzles 42 and 43. A single fan or air 44 isemitted from an air nozzle 45. The fan of air 44 is disposed so that itbisects the angle formed by the two planar fans of apint 40 and 41. Thetwo fan streams of paint converge and are impinged by the air stream 44in an area indicated generally at 47. Both paint streams are broken upinto a fine mist, or fog, of generally uniform paint particles asindicated in FIG. 8. In fact, the atomization is even more efficientthan in the embodiment disclosed in FIGS. and 6 since the air stream isin effect trapped between the two fluid streams and its energy is moreeffectively utilized in breaking up the apint into minute droplets.

The same parameters described above in connection with the methodillustrated in FIGS. 5 and 6 are also applicable to the method disclosedin FIGS. 7 and 8. More particularly, the angles Y and Y between theapint and air streams are in the range of from approximately 30 toapproximately 70. The paint pressure is from 30 to 80 psi, while the airpressure is from 9 to 45 psi at the gun. The ratio of the length of airtravel L, from the nozzle to the zone of impingement compared to the thelength of paint travel from the nozzle to the zone of impingement isapproximately in the range of one-sixth to three-fourths. Also, theactual length of paint travel L is of the range of approximatelythreeeighths to three-fourths inches, while the actual length of airfilm travel L, is approximately one-eighth to three-eighth inches.Furthermore, the ratio of volume of air to quantity of paint applied isthe same as that described above. This ratio is in the range of from 0.2to 0.6 standard cubic feet of air per fluid ounce of paint.

The process described above can also be employed to effect asimultaneous atomizing, mixing and spraying of two different liquids forcoating. More particularly, it has been determined that one type ofliquid can be sprayed from one nozzle and a different type of liquid canbe sprayed from the second nozzle with the result that the coatingdeposited on the work is of a uniform blend of the two coating liquids.

The process of atomization described thus far can be employed by itselfto cause effective application of paint or a similar coating to aproduct. However, the atomization process can also be utilized inconnection with a paint charging step to electrostatically spray paint.In accordance with the present invention, this charging operation iseffected by utilizing the atomizing air as a charge carrier fortransferring charges to the paint particles.

As is shown in FIG. 7, an electrode 50 is disposed in the air streampreferably within the air nozzle 45. This electrode is connected to asource of high DC potential, for example, a potential of the order of 50Kv. It will, of course, be understood that the potential applied to theelectrode 50 can be greater or less than this figure, depending uponsuch variables as the characteristics, e.g. resistivity of the paintbeing applied nature of the article being coated, distance of the gunfrom the article, etc.

The potential applied to electrode 50 causes a corona discharge to beformed surrounding the tip of the electrode. The air stream passesthrough this corona on its path through the nozzle and as a result largenumbers of ions are formed in the stream. These ions, i.e. ionized gasmolecules have relatively high mobility and move primarily under theinfluence of the electrostatic field toward the coating material at arelatively low potential. In practice, the ions thus move toward thepaint which is at a low potential and ultimately attach themselves tothe atomized paint particles.

The two paint stream method illustrated in FIGS. 7 and 8 results in animproved charging efficiency over the one paint stream method shown inFIG. 5. One possible explanation for this is that the paint streamsenvelope the air stream, i.e. are disposed on both sides of it.Consequently, the ions must pass through a paint stream or a fog ofpaint particles in order to reach a ground surface. In this travel thereis a high likelihood that they will attach themselves to one of thepaint particles. In contrast, in the one paint stream method of FIG. 5,the ions can escape to a grounded surface without passing either througha paint stream or a fog of particles, e.g. as shown in FIG. 5 thecharged ions could be attracted to a grounded surface and move off tothe right without ever contacting the paint.

In any event, empirical tests have shown that the two paint fanelectrostatic paint spraying method of FIGS. 7 and 8 as compared to theone paint fan method of FIG. 5 (even when the air stream of the onepaint fan method is ionized).

Another important facet of the present spraying method involves thecontrol of the width of the spray pattern. More particularly, it will beappreciated that articles being sprayed vary in physical dimensions sothat in order to minimize overspray, it is often desirable to alter thesize of the paint spray pattern produced by the gun. The novel manner inwhich this is accomplished in the present invention is diagrammaticallyshown in FIGS. 15 and 16.

FIG. 15 shows a paint spray directed against a target 55. The actualpattern 56 of spray has a width W which in actual practice would beslightly longer than the target 55. We have empirically determined thatthe width of the spray pattern can be varied by changing the includedangle S of the air stream without changing the width of the paintstream.

As shown in FIG. 15, a fan-shaped sheet of air 57 is emitted from anozzle 58. The air impinges upon a fanshaped film of paint 60. It willbe appreciated that this film of paint may be a single film which isprojected at an angle to the air fan as shown in FIGS. 5 and 6, or mayin fact be constituted by two paint films as shown in FIGS. 7 and 8.

In either event, the air is projected from the nozzle in a fan-shapedstream which is shown as having upper and lower edges 61 and 62including an angle S such that the air stream just intercepts the entiresection of the film against which the air stream impinges. Again, itwill be appreciated that in actual practice the angle S would beslightly greater than that shown so that the air stream passes slightlyabove and below the film. (This exact relationship is not shown,however, to simplify the present explanation.)

In practice, the spacing between the paint film 60 and the target 55remains substantially constant. Accordingly, when it is desired to spraya smaller target 55', as shown in FIG. 16, it is desirable to produce apaint pattern 56 having a smaller width W without requiring shifting ofthe gun. In accordance with the present invention, this change in thespray pattern is accomplished by projecting the air fan at a smallerangle S. It will be appreciated that if the angle of the air fan in FIG.15 were reduced with no further change, the air stream would intersectonly a portion of the paint film 60. This would result in substantiallyunatomized, or coarsely atomized, paint and, hence, a defective finish.

In accordance with the present method, this difficulty is avoided andthe paint pattern width is varied without affecting the uniformatomization of all of the paint. Specifically, the size of the paintpattern is altered by making two changes in the air fan. In the firstplace, the included angle of the air stream is reduced from the angle Sto the angle S. In the second place, the internal configuration of thenozzle opening is changed so that the apparent focal point, or pressuresource point, P of the air stream is shifted away from the nozzleopening and away from the paint film to a more remote point as indicatedby P.

More particularly, as shown in FIG. 15, it is apparent that the nozzleopening is formed by the intersection of two segments of circular arcs,an external arc 63 and an internal are 64. In this example, the arcs aredisposed relative to one another so that the nozzle opening encompassesapproximately 180 of the inner are 64. This nozzle functions as thoughthe air emanates from a point source P disposed relatively close to thenozzle opening.

The changed nozzle opening, as shown in FIG. 16, is also formed by theintersection of outer are 63' and inner are 64'. In this case, theradius of the outer are 63' isvthe same as that of are 63 However, theradius of the inner are 64' is appreciably greater than. the are 64. Asa result, the nozzle opening intersects a much smaller portion of theinner are 64'. This nozzle func- .tions as though the air emanates froma point pressure source P spaced an appreciable distance from the nozzleopening andfrom film sheet 60'.

As a result of these concomitant changes, i.e. lessening the includedangle of the air fan while at the same time shifting the apparent focalpoint or apparent point source of the air stream away from the nozzleand paint film, the height of the air fan at its point of intersectionwith the film remains constant. Consequently, by changing the air fan inthis manner without changing any other aspect of the operation of thegun, for example, the paint pressure or paint sheet size, the paintpattern can be compacted or enlarged. A preferred form of nozzleconstruction for effecting these changes in a simple manner isillustrated in FIGS. -14, and the details of construction of this nozzleare explained below.

SPRAY GUN The details of construction of a preferred form of spray gunfor carrying out the present method of paint spraying are shown in FIGS.9-14. As there shown, the spray gun 11 comprises a hollow handle portion66, a barrel or extension portion 67 formed of a suitable insulatingmaterial and mounted forwardly of the handle and a nozzle assembly 68mounted on the forward end of barrel 67.

The nozzle assembly 68 includes two paint nozzles 70 and 71 effective toproject flat fan-shaped sprays of paint toward the center line of thegun as indicated by dotted lines 72 and 73. The gun further includes anair nozzle 74 effective to project a fan-shaped stream of air forwardlyalong the axis of the gun toward the area of intersection of the paintstreams as indicated by line 75. Additionally, the gun includes anelectrostatic charging circuit including a needle electrode 76 forcharging the atomizing air and ultimately causing a charge to be appliedto the atomized paint particles.

Operation of the gun is controlled by a single trigger 77 which iseffective to control flow of paint through a paint valve 78, flow of airthrough air valve 80, and application of electric potential to electrode76 through actuation of switches 81 and 82. The trigger functions tofirst open air valve 80, then open paint valve 78 and finally closeswitch 81. When the trigger is released this sequence is reversed.

More particularly, handle 66 is formed of a suitable conductivematerial, such as aluminum or the like. The handle is hollow and isconfigurated to form a hand grip portion 83, a forwardly extending stockportion 84 and a suspension hook portion 85. A transverse flange isformed at the forward end of the stock for abutment witha mating flangeon the barrel. The barrel and stock flanges are bolted together in aconventional manner. Hand grip portion 83 is provided adjacent its lowerend with an opening 86 for receiving the combined air and electricalinput fitting 87.

' Air is introduced to the gun through an air tube 15 which surroundselectrical cable 17, there being an annular space between the tube walland cable for passage of air from the compressor to the inlet fitting ofthe gun. The hollow interior of the gun is sealed at the cable entrancein any suitable manner, such as by means of an O-ring 90 compressedbetween a shoulder in the gun housing and a threaded cap member 91. Airpasses through an inlet passageway'92 formed in the handle and enters avalve chamber 93 of air valve 80.

This valve includes a reciprocating stem member 94 having an extension95 disposed for abutment with trigger member 77. An intermediate portionof the stem carries an Oring 96 or similar packing member disposedbetween spaced shoulder 97. The inner end of the stem carries a taperedplug 98 adapted to engage a tapered seat to seal off the air flow. Whenthe trigger is depressed, plug 98 is shifted against the force of spring99 from engagement with seat 100 and air is free to flow into internalchamber 101 in the gun handle.

This chamber communicates with a longitudinal bore 102 in the stock anda continuation of this bore 103 formed in the barrel member. Thischamber surrounds a sleeve 104 which is formed of insulating materialand is supported in mounting spiders 105 and 106. The forward end ofbore 103 communicates with a longitudinal bore 107 formed in nozzlesupport member 108 which carries the paint and air nozzles. Nozzlesupport member 108 is preferably formed of an insulating material suchas Delrin. Support member 108 is mountedon the front end of barrelmember 67'by means of a threaded cap 109 which is coupled to themounting member by a retaining ring 119 fitted in opposed grooves in thecap and mounting member. Cap 109 engages threaded extension 129 on thebarrel.

Support member 108 is provided with a circular plugreceiving opening110. This opening 110 houses a generally cylindrical air nozzle plug 111which is preferably made of a plastic material, e.g. Delrin. Nozzle plug111 includes an annular peripheral wall 112 having an arcuate inletopening 113 which communicates with a vertical central chamber 114. Thelower end of the plug is closed by a solid circular wall 115, while thetop of the plug is closed by a cap 116 which is press fit or otherwisesecured to the top of the plug. The cap seals The peripheral wall of theplug member opposite entrance slot 113 is provided with three parallelspaced, rectangular openings 120, 121 and 122. The plug can be rotatedto selectively align any one of these openings with front opening 123 inmember 108. The selection of the particular nozzle opening 120, 121 and122 disposed in registry with front opening 123 of the stationarysupport member 108 provides the means for varying the air stream to varythe paint spray pattern in the manner shown diagrammatically in FIGS. 15and 16.

More particularly, opening 120 is effective to provide the widest angleof air spray fan and, hence, the widest paint spray pattern. Similarly,opening 121 is effective to provide the narrowest air spray fan and,hence the narrowest paint spray pattern. Nozzle opening 122 is effectiveto provide an air spray fan and paint spray pattern of intermediatesize.

It will be noted that nozzle opening 120 is formed by a semi-cylindricalinternal cut 124 formed in peripheral wall 112, the axis of cut 124being horizontal. This cut is intersected by a segmental disc-like cut125 oriented in a vertical plane and extending inwardly from the outerperiphery of wall 112 internally along a radius of the plug member.

In one preferred embodiment of the plug member, the disc-like cut 125has a 0.375 inch radius with a center located 0.178 inch outwardly fromthe periphery of the plug wall. Internal cut 124 has aseven-sixty-fourths inch radius located inwardly 0.169 inch from theperiphery of the plug. This nozzle opening has been found effective toemit a fan-shaped stream of air having an included angle ofapproximately 94. Hydraulically, this nozzle opening functions generallyas though there were a point source of gas pressure located at point P1approximately one-fourth inch inwardly from the periphery of the plugmember.

Slot 121 is formed by an internal semi-cylindrical cut 126 formed inperipheral wall 112 along a horizontal axis. Cut 126 is intersected by ahorizontal disc-like cut 127. Disc-like cut 127 extends radiallyinwardly from the outer periphery of wall 112. In one preferredembodiment of plug, the disc-like cut 127 has a 0.375 radius with thecenter located 0.219 inch outwardly from the periphery of the plug wall.

Internal cut 126 has a radius of 0.203 inch with the center of the cutbeing located 0.263 inch from the periphery of the plug. This nozzleopening has been found to emit a fan-shaped stream of air having anincluded angle of approximately 36. This nozzle functions generally asthough the air emitted from it emanated from a point source P3 disposedsubstantially further from the peripheral wall than point P1 (e.g.,approximately four times as far).

In order to maintain the volume of air emitted from nozzle openings 120and 121 substantially equal, the width of nozzle opening 121 is madeslightly narrower than the width of nozzle opening 120 so that thecrosssectional area of the opening is constant. Thus, in one preferredembodiment, the width of nozzle opening 120 is made equal to 0.074 inch,while the width of nozzle opening 121 is made equal to 0.065 inch.

The third, or intermediate size, nozzle opening 122 is similarly formed,i.e. this nozzle opening is formed from a segment ofa cylindricallyinternal cut 128 intersected by a vertical disc-like cut 130, disc-likecut 130 extending inwardly along a radius from the outer peripheral wall112. In one preferred embodiment, the

cut has a 0.375 radius with a center located 0.168 inch from theperiphery of the plut. Inner cut 128 has a radius of 0.156 inch located0.216 inch from the periphery of the disc. This nozzle opening emits afanshaped stream ofir having an included angle of approximately 64. Airis emitted from this nozzle in generally the same manner as though theair flowed from a point source P2 located of the order of twice thedistance from the periphery of the plug as point P1. In this preferredembodiment the pressure of the air applied to the gun is relatively low,for example, of the order of 9-45 psi at the gun. The exit velocity ofthe air is approximately sonic. The distance, in the preferred gun, ofair travel L to the point of impingement of the air and paint streams isapproximately three-sixteenth inch.

Paint is supplied to the gun from pump 12 through tube 14. This tube iscoupled to the gun through fitting 131 which communicates with alongitudinal paint passage 132 formed in extension member 67. Passage132 communicates with the seat area 133 of paint valve 78. This seatarea is engaged by a spherical head 134 of valve stem member 135. Thisvalve stem member reciprocates longitudinally to shift the head 134toward and away from the seat member and is spring-urged toward the seatby means of a compression spring 136.

The valve is adapted to be opened by pressure on trigger 77. When thetrigger is pivoted toward the handle member about pivot pin 137 whichsupports the upper end of the trigger, the trigger engages a shoulder138 secured to stem 135, forcing the stem rearwardly to open the paintvalve. With paint valve 78 open, paint is free to flow throughlongitudinal conduit 140 into annular passageway 141 and from thispassageway into axial angulated bores 142 and 143 formed in nozzlesupport member 108. These bores communicate with paint nozzle assemblies70 and 71.

More particularly, bores 142 and 143 are aligned with inlets 144 and 145in cylindrical members 146 and 147. Each of these cylinders is formedwith an internal passageway 148 and a seat 150 for a check valve formedby ball member 151. Each of the balls 151 is spring-urged against theseat by means of a spring 152 bearing against a thrust washer 153mounted within a chamber 154 in cylindrical members 146, 147. Each ofthe chambers opens into an axial passageway 155 communicating with anaxial bore 156 in tubular nozzle member 157. Each of the nozzle membersis preferably formed of a suitable plastic material, such as Delrin.

The fluid discharge passageway in each of the nozzles is formed by aV-shaped cut 158 extending inwardly from a periphery of the wall toapproximately the center line of the tube. Each of the V-shaped cuts 158includes a rearward wall 160 and a forward wall 161. As

shown in FIG. 10, each nozzle 157 is angulated, or

tilted, slightly outwardly relative to the axis of passageway 155. Thistilting enables the nozzle to direct the paint stream at the desiredangle relative to the air fan.

More particularly, each nozzle 157 is effective to emit a thinsubstantially planar fan-shaped stream of paint at an angle ofapproximately 60 to the axis of bore 155 which is parallel to the axisof the gun. Consequently, this fan-shaped paint stream is impinged bythe fan-shaped air stream at approximately the same angle, i.e. atapproximately 60. In this preferred embodiment, the length of painttravel L from the nozzle to the zone of impingement of the paint and airstreams is approximately five-eighth inch.

In accordance with the present invention, the ends of axial bores 156 ineach of the nozzle tubes 157 is closed by a spring-loaded plug 159.These plugs are secured to angulated spring members 162 in any suitablemanner; for example, as shown in FIG. 10, plug 158 passes through asmall bore in a portion of arm 162 and has an overturned head 163effective to clamp the plug to the arm. Both plugs 159 and springmembers 162 are preferably formed of a uitable plastic material. ARms162 include a transverse section 164 and a foot portion 165 which ismounted upon the support member 108 in anysuitable manner, such as bymeans of bolts 166.

Each of the spring members 162 also includes an overturned flangeportion 167 by means of which the spring arm can be pulled outwardly todisengage the plug from the seat formed in the end of the associatedtube member 157. In normal operation, the spring force is sufficient tomaintain the plug in sealing engagement with the end of the tube 157.However, in the event that the nozzle should become clogged, the passagecan readily be cleared by graspingflange portion 163 to pull the springarm and plug outwardly, opening the end of the tube. Trigger 77 is thendepressed to cause paint to be discharged from the end of the tuberemoving whatever impediment had accumulated in the tube section.

The electrical input to the gun is preferably through a high resistancecable 17. The details of construction of one preferred form of cable aredisclosed in Rosen U.S. Pat. NO. 3,348,186. The remote end of this cableis connected toa power pack 16 effective to develop a high DC potential,for example, 50,000 volts. Cable 17 enters the gun through the interiorof fitting 87 and passes upwardly through a hollow section 170 of thehandle. The cable is flexible and is bent rearwardly around shoulder 171at the junction of the hand grip portion 83 and the stock portion 84toward the rear wall 172 of the stock. The cable is then bent forwardlyand is inserted into insulating sleeve l04,the cable being looselyreceived in the sleeve so that it is free to move relative thereto. Theforward end of the cable is provided with a contact button 173. disposedfor mating contact with a similar contact button 174 provided on therear end of cylindrical resistor 175.

This resistor is preferably sealed in the end of sleeve 104 and has anelectrical resistance of the order of 75 megohms. The forward end ofresistor 175 is in electrical contact with a bolt 176 passing inwardlythrough a cap member 177 enclosing the forward end of sleeve 104.

The head 180 of bolt 176 is engaged by a contact spring 178 which iscompressed between the head of the bolt and a head 181 formed onelectrode 76. Electrode 76 is in the form of an elongated pin supportedin axial alignment with the air nozzle by means ofa cruciform insulatingmember 182. This cruciform insulating member includes a central bore 183into which the pin is press fit. The cruciform member is rigidly mountedin the central opening 107 in support member 108.

Electrode 76 extends forwardly through entrance opening 113 in the airnozzle member and extends forwardly to a position just inside theperipheral wall 112 carrying the three nozzle openings 120, 121, and122. In normal operation, this electrode is charged to a suitablepotential of the order, for example, of 40,000 volts. A corona isestablished surrounding the tip of the electrode. The stream of airflowing through the nozzle surrounds the electrode and passes throughthe corona prior to the time it is discharged from the nozzle opening.As the air passes through the corona gas molecules are ionized and dustparticles are charged. These ions and charged particles move forwardlyunder the influence of the electrostatic field forces toward a lowerpotential region of the field constituted by the paint films andatomized particles. There the charges attach themselves to the paintparticles to form the charged paint spray.

One of the advantages of this paint charging device is that the paintsupply in conduit 14 does not become charged so that the entire paintsupply system, including tube 14, pump 12 and the paint supply tank 13,remain at or very near ground potential. In fact, in the embodimentshown the paint supply system is grounded through needle and handlemember 66 which is conventionally grounded in use. This greatlysimplifies the problem of insulating the paint supply system andeliminates the dangers common in many prior art systems due to chargeaccumulation in the paint supply system.

In addition to the elements described above, the electrical chargingcircuit includes a safety circuit for preventing application of power tothe cable in the event that resistor is removed from the gun and the gunreassembled without replacing the resistor.

More particularly, as is best shown in FIG. 9, the cable 17 forms arearwardly extending resilient bend adjacent to rear wall 172 of thestock. An actuating arm 191 is pivoted about pin 192 in the stockportion of the gun and is interposed between cable bend 190 and rearwall 172. This arm includes a forwardly extending link portion 189 whichis attached to one end of tension spring 193, the other end of thespring being secured to a stationary bracket 194.

Bracket 194 carries snap-action microswitches 81 and 81. Microswitch 82is normally closed, while microswitch 81 is normally open. A spring arm195 is disposed for engagement with actuating plunger 196 of microswitch82. This spring arm is adapted to be shifted with link 189, for example,by engagement with a shoulder 197 carried by the link.

So long as the cable 17 is positioned rearwardly as shown in FIG. 9,plunger 196 is not depressed and switch 82 remains closed. In normaloperation of the gun, the cable is held in this position against forwardmovement by the presence of resistor 175. However, if resistor 175 andsleeve 104 are not present in the gun, spring 193 acting upon arm 191forces the cable forwardly within conduit 103. This forward movement ofarm 191 causes arm 195 to open switch 82.

As is shown in FIG. 17, switch 82 is connected in series with switch 81and a coil 198 of relay 200. Switch 81 is normally open switch adaptedto be closed upon actuation'of trigger 77. More particularly,microswitch 81 includes an actuating plunger 201 adapted to be engagedby 5 spring arm 202. This arm in turn is positioned for contact with ahead 203 formed on the continuation of stem member 135.

When trigger 77 is depressed, the stem and its extension are shiftedrearwardly so that head 203 bends spring arm 202, closing microswitch81. When both microswitch 81 and 82 are closed, relay 200 is energizedto complete a circuit to power pack 16. This power pack is theneffective to apply a potential to cable 17 and, hence, to electrode 76.

The safety circuit just described is also effective to preventapplication of power to the cable when the nozzle assembly is removedfrom the gun. More particularly, as is shown in FIG. 9, tube 104 issupported in the surrounding bores in the stock member and barrel bymeans of low friction spiders 105 and 106. The tube is normally retainedin its retracted position shown in FIG. 9 by the abutment of spider 182with the end of cap member 177. However, when the nozzle mountingmemberl08 is removed by unthreading cap 109' from the threaded extension129 on the barrel member, the restraint on forward movement of thesleeve is removed, The sleeve is then shifted forwardly under theinfluence of spring 193 acting on the cable member.

As the cable member is shifted to the left, arm 191 is shifted forwardlycausing arm 195 to open switch 82 preventing energization of the powerpack and thereby preventing application of potential to cable 17. At thesame time, forward movement of sleeve 104 is effective to provide asecond function in that it automatically seals the air chamber and endof the resistor or electrical conduit from contamination. Moreparticularly, as best shown in FIGS. 9 and 10, the forward end of cap177 is tapered to form a seat 204. This seat is effective to engage amating tapered seat 205 formed in the barrel 67 when sleeve 104 isshifted forwardly, i.e. to the left in FIG. 10.

When the nozzle is reassembled, spider 182 engages cap 177 forcing thecap away from the seat 205 to reopen the air conduit. At the same time,the cable 17 is shifted rearwardly so that ben 190 causes arm 191 topivot, thereby reclosing switch 82 to permit reenergization of the powrpack andeable 17 when trigger 77 is depressed.

The construction of the gun as described above also incorporates twoadditionalsafety features. In the first place, switches 81 and 82 andthe other electrical contacts such as those between the cable andresistor occur in an enclosed or pressurized explosive-proof chamber.Moreover, this chamber is continuously purged to remove any accumulatedgases by the flow of the air utilized to atomize the paint.

From the foregoing disclosure of the general principles of the presentinvention and the above description of a preferred embodiment, thoseskilled in the art will readily comprehend various modifications towhich this invention is susceptible.

For example, while the air fan and paint fan streams have been describedas being substantially planar, it is contemplated that the paint fansmay be slightly arcuate, i.e. in the form of thin bowed sheets.Moreover, if a gun is to be utilized for atomizing, mixing and sprayingtwo different liquids by spraying one liquid from one nozzle and anotherliquid from the other nozzle, it is apparent that a separate supply linemust be provided for each nozzle. This can readily be accomplished byessentially duplicating the liquid supply system shown while eliminatingthe conduit which now interconnects the two nozzles. Also while air hasbeen described as the atomizing gas, it will be appreciated that in someparticular installations other gases could be employed. Accordingly, theterm air" as used in the following claims should be interpreted asincluding other gases as well.

Accordingly, we desire to be limited only by the scope of the followingclaims in which it is to be understood that the term paint" is used inthe generic sense to cover fqnish coatings of the type described aboveand in which the term gun is used generically to cover either a handspray gun or a mechanicallysupported control spray device.

Having described our invention, we claim:

1. The method of spraying paint which comprises the steps of:

projecting a flat fan of paint,

projecting a fan of air,

causing the fan of air to impinge upon the fan of paint at a substantialangle of from approximately 30 to approximately the fan of air being atleast as wide at the zone of air-paint impingement as the fan of paint,whereby the air fan is effective to atomize the paint to form a spray,

and projecting said spray against a workpiece to be coated.

2. The method of claim 1 in which the air is projected from an airnozzle and the paint is projected from a paint nozzle, and the length ofair travel from the air nozzle to the zone of paint air impingement isfrom approximately one-sixth to three-fourths the length of paint travelfrom the paint nozzle to the zone of airpaint impingement.

3. The method of claim I in which air is projected from an air nozzleand paint is projected from a paint nozzle and the length of air flowfrom the nozzle to the zone of air-paint impingement is fromapproximately one-eighth inch to three-eighths inch and the length ofpaint travel from the paint nozzle to the zone of airpaint impingementis approximately three-eighths to three-fourths inches.

4. The method of claim 1 in which the air flows in a ratio of fromapproximately 0.2 standard cubic feet of air per minute per fluid ounceof paint per minute to approximately 0.6 standard cubic feet of air perminute per fluid ounce of paint per minute.

5. The method of claim 1 in which the air pressure is from approximately9 pounds to 45 pounds per square inch at the gun.

6. The method of claim 5 in which the paint pressure is approximatelyfrom 30 to pounds per square inch.

7. The method of claim 4 in which the air pressure is from approximately9 pounds to 45 pounds per square inch at the gun.

8. The method of claim 7 in which the paint pressure is approximatelyfrom 30 to 80 pounds per square inch.

9. The method of claim 1 in which the fan of paint is in the form of acontinuous sheet having a thin center web and thickened streamerportions along both edges.

10. The method of claim 9 in which the fan of air is non-uniform and hasmass higher flow rates in the areas of impingement upon the streamerportions than in the area impinging upon the center web of the paintfan.

11. The method of claim 10 in which the air flows in a ratio of fromapproximately 0.2 standard cubic feet of air per minute per fluid ounceof paint per minute to approximately 0.6 standard cubic feet of air perminute per fluid ounce of paint per minute.

12. The method of claim 10 in which the air pressure is fromapproximately 9 pounds to 45 pounds per square inch at the gun and thepaint pressure is approximately from 30 to 80 pounds per square inch.

13. The method of claim 12 in which air is projected from an air nozzleand paint is projected from a paint nozzle and the length of air flowfrom the nozzle to the zone of air-paint impingement is fromapproximately one-eighth inch to three-eighths inch and the length ofpaint travel from the paint nozzle to the zone of airpaint impingementis approximately three-eighths to three-fourths inches.

14. The method of spraying paint which comprises the steps of projectinga flat fan of air;

projecting two flat fans of paint,

fans of paint being projected toward the fan of air from opposite sidesthereof and impinging the fan of air in substantially the same area,

each of the fans of paint impinging upon the fan of air at a substantialangle of from approximately 30 to approximately 70,

the fan of air being at least as wide at the zone of airpaintimpingement as the fans of paint, whereby the air fan is effective toatomize both fans of paint to form a spray and,

projecting said spray against a workpiece to be coated.

15. The method of claim 14 in which air is projected from an air nozzleand each fan of paint is projected from a paint nozzle, and the lengthof air travel from the air nozzle to the zone of paint-air impingementis from approximately one-sixth to three-fourths the length of painttravel from the paint nozzle to the zone of air-paint impingement.

16. The method of claim 14 in which air is projected from an air nozzleand each fan of paint is projected from a paint nozzle and the length ofair flow from the nozzle to the zone of air-paint impingement is fromapproximately one-eighth inch to three-eighths inch and the length ofpaint travel from the paint nozzle to the zone of air-paint impingementis approximately threeeighths to three-fourths inches.

17. The method of claim 14 in which the air flows in a ratio of fromapproximately 0.2 standard cubic feet of air per minute per fluid ounceof paint per minute to approximately 0.6 standard cubic feet of air perminute per fluid ounce of paint per minute.

18. The method of claim 17 in which the air pressure is fromapproximately 9 pounds to 45 pounds per square inch at the gun and thepaint pressure is approximately from 30 to 80 pounds per square inch.

19. The method of claim 14 in which the air pressure is fromapproximately 9 pounds to 45 pounds per square inch at the gun and thepaint pressure is approximately from 30 to 80 pounds per square inch.

20. The method of claim 14 in which each fan of paint is in the form ofa continuous sheet having a thin center web and thickened streamerportions along both edges.

21. The method of claim 20 in which the fan of air is non-uniform andhas mass higher flow rates in the areas of impingement upon the streamerportions than in the area impinging upon the center web of the paintfans.

22 The method of claim 21 in which the air flows in a ratio of fromapproximately 0.2 standard cubic feet of air per minute per fluid ounceof paint per minute to approximately 0.6 standard cubic feet of air perminute per fluid ounce of paint per minute.

23. The method of claim 21 in which the air pressure is fromapproximately 9 pounds to 45 pounds per square inch at the gun and thepaint pressure is approximately from to 80 pounds per square inch.

24. The method of claim 23 in which air is projected from an air nozzleand each fan of paint is projected from a paint nozzle and the length ofair flow from the nozzle to the zone of air-paint impingement is fromapproximately one-eighth inch to three-eighths inch and the length ofpaint travel from the paint nozzle to the zone of air-paint impingementis approximately threeeighths to three-fourths inches.

25. The method of simultaneously mixing and spraying paint whichcomprises the step of projecting a flat fan of air, projecting two flatfans of paint, each of said flat fans of paint being of a differentcolor,

the fans of paint being projected toward the fan of air from oppositesides thereof and impinging the fan of air in substantially the samearea,

. each of the fans of paint impinging upon the fan of air at asubstantial angle of from approximately 30 to approximately the fan ofair being at least as wide at the zone of airpaint impingement as thefans of paint, whereby the air fan is effective to atomize both fans ofpaint to form a spray and,

projecting said spray against a workpiece to be coated.

26. The method of spraying paint which comprises the steps of:

projecting a flat fan of paint from a paint nozzle,

projecting a fan of air from an air nozzle, causing the fan of air toimpinge upon the fan of paint at a substantial angle, the fan of airbeing at least as wide at the zone of air-paint impingement as the fanof paint, and the length of air travel from the air nozzle to the zoneof paint-air impingement is from approximately one-sixth tothree-fourths the length of paint travel from the paint nozzle to thezone of air-paint impingement, whereby the air fan is effective toatomize the paint to form a spray,

and projecting said spray against a workpiece to be coated.

27. The method of spraying paint which comprises the steps of:

projecting a flat fan of paint from a paint nozzle,

projecting a fan of air from an air nozzle,

causing the fan of air to impinge upon the fan of paint at a substantialangle, the fan of air being at least as wide at the zone of air-paintimpingement as the fan of paint, and the length of air flow from thenozzle to the zone of air-paint impingement is from approximatelyone-eighth inch to three-eighths inch and the length of paint travelfrom the paint nozzle to the zone of air-paint impingement isapproximately three-eighths to three-fourths inches, whereby the air fanis effective to atomize the paint to form a spray,

and projecting said spray against a workpiece to be coated. 28. Themethod of spraying paint which comprises the steps of:

projecting a flat fan of paint from a paint nozzle,

projecting a fan of air from an airnozzle,

causing the fan of air to impinge upon the fan of paint at a substantialangle, the fan of air being at least as wide at the zone of air-paintimpingement as the fan of paint, and the air flows in a ratio of fromapproximately 0.2 standard cubic feet of air per minute per fluid ounceof paint per minute to approximately 0.6 standard cubic feet of air perminute per fluid ounce of paint per minute, whereby the air fan iseffective to atomize the paint to form a spray,

and projecting said spray against a workpiece to be coated.

29. The method of spraying paint which comprises the steps of:

projecting a flat fan of paint from a paint nozzle,

projecting a fan of air from an air nozzle,

causing the fan of air to impinge upon the fan of paint at a substantialangle, the fan of air being at least as wide at the zone of air-paintimpingement as the fan of paint, and the air pressure is fromapproximately 9 pounds to 45 pounds per square inch at the gun, wherebythe air fan is effective to atomize the paint to form a spray,

and projecting said spray against a workpiece to be coated. 30. Themethod of varying the size of a paint spray pattern which comprises,

the steps of projecting a flat fan of paint, projecting a fan of airfrom an air nozzle, causing the fan of air to impinge upon the fan ofpaint at a substantial angle, the fan of air being at least as wide atthe zone of air-paint impingement as the fan of paint, whereby the airfan is effective to atomize the paint to form a spray pattern and,

selectively increasing or decreasing the included angle of the air fanto increase or decrease the width of the paint spray pattern.

31. The method of claim 30 in which the fan of air flows as though itemanates from a ,point pressure source and the point pressure source isshifted away from the zone of impingement of the air-paint when theincluded angle of the air fan is decreased, whereby the width of the airfan at the zone of impingement with the air-paint remains substantiallyconsistent.

32. The method of spraying paint which comprises the steps of projectinga flat fan of air from an air nozzle,

projecting two flat fans of paint from two paint nozzles,

the fans of paint being projected toward the fan of air from oppositesides thereof and impinging the fan of air in substantially the samearea,

each of the fans of paint impinging upon the fan of air at a substantialangle,

the fan of air being at least as wide at the zone of airpaintimpingement as the fans of paint, whereby the air fan is effective toatomize both fans of paint to form a spray and,

the air pressure is from approximately 9 pounds to 45 pounds per squareinch at the gun, and

projecting said spray against a workpiece to be coated.

33. The method of spraying paint which comprises the steps of:

projecting a flat fan of paint,

said fan of paint being in the form of a continuous sheet having a thincenter web and thickened streamer portions along both edges,

projecting a fan of air,

causing the fan of air to impinge upon the fan of paint 6 whereby theair fan is effective to atomize the paint to form a spray,

and projecting said spray against a workpiece to be coated.

34. The method of spraying paint which comprises the steps of projectinga flat fan of air from an air nozzle,

projecting two flat fans of paint from two paint nozzles,

the fans of paint being projected toward the fan of air from oppositesides thereof and impinging the fan of air in substantially the samearea,

each of the fans of paint impinging upon the fan of air at a substantialangle,

the fan of air being at least as wide at the zone of airpaintimpingement as the fans of paint, whereby the air fan is effective toatomize both fans of paint to form a spray, each fan of paint being inthe form of a continuous sheet having a thin center web and thickenedstreamer portions along both edges, and

projecting said spray against a workpiece to be coated.

35. The method of spraying paint which comprises the steps of projectinga flat fan of air from an air nozzle,

projecting two flat fans of paint from two paint nozzles,

each fan of paint being in the form of a continuous sheet having a thincenter web and thickened streamer portions along both edges,

the fans of paint being projected toward the fan of air from oppositesides thereof and impinging the fan of air in substantially the samearea,

each of the fans of paint impinging upon the fan of air at a substantialangle,

the fan of air being at least as wide at the zone of airpaintimpingement as the fans of paint, whereby the air fan is effective toatomize both fans of paint to form a spray,

the fan of air being non-uniform and having higher flow rates in theareas of impingement upon the streamer portions than in the areaimpinging upon the center web of the paint fans, and

projecting said spray against a workpiece to be coated.

36. The method of spraying paint which comprises the steps of projectinga flat fan of air from an air nozzle,

projecting two flat fans of paint from two paint nozzles,

the fans of paint being projected toward the fan of air from theopposite sides thereof and impinging the fan of air in substantially thesame area,

each of the fans of paint impinging upon the fan of air at a substantialangle,

the fan of air being at least as wide at the zone of airpaintimpingement as the fans of paint, whereby the air fan is effective toatomize both fans of paint to form a spray,

the air flowing in a ratio of from approximately 0.2

standard cubic feet of air per minute per fluid ounce of paint perminute to approximately 0.6 standard cubic feet of air per minute perfluid ounce of paint per minute, and

projecting said spray against a workpiece to be coated.

37. The method of claim 33 in which the paint pressure is fromapproximately 30 to pounds per square inch.

l t i

1. The method of spraying paint which comprises the steps of: projectinga flat fan of paint, projecting a fan of air, causing the fan of air toimpinge upon the fan of paint at a substantial angle of fromapproximately 30* to approximately 70*, the fan of air being at least aswide at the zone of airpaint impingement as the fan of paint, wherebythe air fan is effective to atomize the paint to form a spray, andprojecting said spray against a workpiece to be coated.
 2. The method ofclaim 1 in which the air is projected from an air nozzle and the paintis projected from a paint nozzle, and the length of air travel from theair nozzle to the zone of paint - air impingement is from approximatelyone-sixth to three-fourths the length of paint travel from the paintnozzle to the zone of air-paint impingement.
 3. The method of claim 1 inwhich air is projected from an air nozzle and paint is projected from apaint nozzle and the length of air flow from the nozzle to the zone ofair-paint impingement is from approximately one-eighth inch tothree-eighths inch and the length of paint travel from the paint nozzleto the zone of air-paint impingement is approximately three-eighths tothree-fourths inches.
 4. The method of claim 1 in which the air flows ina ratio of from approximately 0.2 standard cubic feet of air per minuteper fluid ounce of paint per minute to approximately 0.6 standard cubicfeet of air per minute per fluid ounce of paint per minute.
 5. Themethod of claim 1 in which the air pressure is from approximately 9pounds to 45 pounds per square inch at the gun.
 6. The method of claim 5in which the paint pressure is approximately from 30 to 80 pounds persquare inch.
 7. The method of claim 4 in which the air pressure is fromapproximately 9 pounds to 45 pounds per square inch at the gun.
 8. Themethod of claim 7 in which the paint pressure is approximately from 30to 80 pounds per square inch.
 9. The method of claim 1 in which the fanof paint is in the form of a continuous sheet having a thin center weband thickened streamer portions along both edges.
 10. The method ofclaim 9 in which the fan of air is non-uniform and has mass higher flowrates in the areas of impingement upon the streamer portions than in thearea impinging upon the center web of the paint fan.
 11. The method ofclaim 10 in which the air flows in a ratio of from approximately 0.2standard cubic feet of air per minute per fluid ounce of paint perminute to approximately 0.6 standard cubic feet of air per minute perfluid ounce of paint per minute.
 12. The method of claim 10 in which theair pressure is from approximately 9 pounds to 45 pounds per square inchat the gun and the paint pressure is approximately from 30 to 80 poundsper square inch.
 13. The method of claim 12 in which air is projectedfrom an air nozzle and paint is projected from a paint nozzle and thelength of air flow from the nozzle to the zone of air-paint impingementis from approximately one-eighth inch to three-eighths inch and thelength of paint travel from the paint nozzle to the zone of air-paintimpingement is approximately three-eighths to three-fourths inches. 14.The method of spraying paint which comprises the steps of projecting aflat fan of air; projecting two flat fans of paint, fans of paint beingprojected toward the fan of air from opposite sides thereof andimpinging the fan of air in substantially the same area, each of thefans of paint impinging upon the fan of air at a substantial angle offrom approximately 30* to approximately 70*, the fan of air being atleast as wide at the zone of air-paint impingement as the fans of paint,whereby the air fan is effective to atomize both fans of paint to form aspray and, projecting said spray against a workpiece to be coated. 15.The method of claim 14 in which air is projected from an air nozzle andeach fan of paint is projected from a paint nozzle, and the length ofair travel from the air nozzle to the zone of paint-air impingement isfrom approximately one-sixth to three-fourths the length of paint travelfrom the paint nozzle to the zone of air-paint impingement.
 16. Themethod of claim 14 in which air is projected from an air nozzle and eachfan of paint is projected from a paint nozzle and the length of air flowfrom the nozzle to the zone of air-paint impingement is fromapproximately one-eighth inch to three-eighths inch and the length ofpaint travel from the paint nozzle to the zone of air-paint impingementis approximately three-eighths to three-fourths inches.
 17. The methodof claim 14 in which the air flows in a ratio of from approximately 0.2standard cubic feet of air per minute per fluid ounce of paint perminute to approximately 0.6 standard cubic feet of air per minute perfluid ounce of paint per minute.
 18. The method of claim 17 in which theair pressure is from approximately 9 pounds to 45 pounds per square inchat the gun and the paint pressure is approximately from 30 to 80 poundsper square inch.
 19. The method of claim 14 in which the air pressure isfrom approximately 9 pounds to 45 pounds per square inch at the gun andthe paint pressure is approximately from 30 to 80 pounds per squareinch.
 20. The method of claim 14 in which each fan of paint is in theform of a continuous sheet having a thin center web and thickenedstreamer portions along both edges.
 21. The method of claim 20 in whichthe fan of air is non-uniform and has mass higher flow rates in theareas of impingement upon the streamer portions than in the areaimpinging upon the center web of the paint fans.
 22. The method of claim21 in which the air flows in a ratio of from approximately 0.2 standardcubic feet of air per minute per fluid ounce of paint per minute toapproximately 0.6 standard cubic feet of air per minute per fluid ounceof paint per minute.
 23. The method of claim 21 in which the airpressure is from approximately 9 pounds to 45 pounds per square inch atthe gun and the paint pressure is approximately from 30 to 80 pounds persquare inch.
 24. The method of claim 23 in which air is projected froman air nozzle and each fan of paint is projected from a paint nozzle andthe length of air flow from the nozzle to the zone of air-paintimpingement is from approximately one-eighth inch to three-eighths inchand the length of paint travel from the paint nozzle to the zone ofair-paint impiNgement is approximately three-eighths to three-fourthsinches.
 25. The method of simultaneously mixing and spraying paint whichcomprises the step of projecting a flat fan of air, projecting two flatfans of paint, each of said flat fans of paint being of a differentcolor, the fans of paint being projected toward the fan of air fromopposite sides thereof and impinging the fan of air in substantially thesame area, each of the fans of paint impinging upon the fan of air at asubstantial angle of from approximately 30* to approximately 70*, thefan of air being at least as wide at the zone of air-paint impingementas the fans of paint, whereby the air fan is effective to atomize bothfans of paint to form a spray and, projecting said spray against aworkpiece to be coated.
 26. The method of spraying paint which comprisesthe steps of: projecting a flat fan of paint from a paint nozzle,projecting a fan of air from an air nozzle, causing the fan of air toimpinge upon the fan of paint at a substantial angle, the fan of airbeing at least as wide at the zone of air-paint impingement as the fanof paint, and the length of air travel from the air nozzle to the zoneof paint-air impingement is from approximately one-sixth tothree-fourths the length of paint travel from the paint nozzle to thezone of air-paint impingement, whereby the air fan is effective toatomize the paint to form a spray, and projecting said spray against aworkpiece to be coated.
 27. The method of spraying paint which comprisesthe steps of: projecting a flat fan of paint from a paint nozzle,projecting a fan of air from an air nozzle, causing the fan of air toimpinge upon the fan of paint at a substantial angle, the fan of airbeing at least as wide at the zone of air-paint impingement as the fanof paint, and the length of air flow from the nozzle to the zone ofair-paint impingement is from approximately one-eighth inch tothree-eighths inch and the length of paint travel from the paint nozzleto the zone of air-paint impingement is approximately three-eighths tothree-fourths inches, whereby the air fan is effective to atomize thepaint to form a spray, and projecting said spray against a workpiece tobe coated.
 28. The method of spraying paint which comprises the stepsof: projecting a flat fan of paint from a paint nozzle, projecting a fanof air from an air nozzle, causing the fan of air to impinge upon thefan of paint at a substantial angle, the fan of air being at least aswide at the zone of air-paint impingement as the fan of paint, and theair flows in a ratio of from approximately 0.2 standard cubic feet ofair per minute per fluid ounce of paint per minute to approximately 0.6standard cubic feet of air per minute per fluid ounce of paint perminute, whereby the air fan is effective to atomize the paint to form aspray, and projecting said spray against a workpiece to be coated. 29.The method of spraying paint which comprises the steps of: projecting aflat fan of paint from a paint nozzle, projecting a fan of air from anair nozzle, causing the fan of air to impinge upon the fan of paint at asubstantial angle, the fan of air being at least as wide at the zone ofair-paint impingement as the fan of paint, and the air pressure is fromapproximately 9 pounds to 45 pounds per square inch at the gun, wherebythe air fan is effective to atomize the paint to form a spray, andprojecting said spray against a workpiece to be coated.
 30. The methodof varying the size of a paint spray pattern which comprises, the stepsof projecting a flat fan of paint, projecting a fan of air from an airnozzle, causing the fan of air to impinge upon the fan of paint at asubstantial angle, the fan of air being at least as wide at the zone ofair-paint impingement as the fan of paint, whereby the air fan iseffective to atomize The paint to form a spray pattern and, selectivelyincreasing or decreasing the included angle of the air fan to increaseor decrease the width of the paint spray pattern.
 31. The method ofclaim 30 in which the fan of air flows as though it emanates from apoint pressure source and the point pressure source is shifted away fromthe zone of impingement of the air-paint when the included angle of theair fan is decreased, whereby the width of the air fan at the zone ofimpingement with the air-paint remains substantially consistent.
 32. Themethod of spraying paint which comprises the steps of projecting a flatfan of air from an air nozzle, projecting two flat fans of paint fromtwo paint nozzles, the fans of paint being projected toward the fan ofair from opposite sides thereof and impinging the fan of air insubstantially the same area, each of the fans of paint impinging uponthe fan of air at a substantial angle, the fan of air being at least aswide at the zone of air-paint impingement as the fans of paint, wherebythe air fan is effective to atomize both fans of paint to form a sprayand, the air pressure is from approximately 9 pounds to 45 pounds persquare inch at the gun, and projecting said spray against a workpiece tobe coated.
 33. The method of spraying paint which comprises the stepsof: projecting a flat fan of paint, said fan of paint being in the formof a continuous sheet having a thin center web and thickened streamerportions along both edges, projecting a fan of air, causing the fan ofair to impinge upon the fan of paint at a substantial angle, while saidfan is substantially planar, the fan of air being at least as wide atthe zone of air-paint impingement as the fan of paint, whereby the airfan is effective to atomize the paint to form a spray, and projectingsaid spray against a workpiece to be coated.
 34. The method of sprayingpaint which comprises the steps of projecting a flat fan of air from anair nozzle, projecting two flat fans of paint from two paint nozzles,the fans of paint being projected toward the fan of air from oppositesides thereof and impinging the fan of air in substantially the samearea, each of the fans of paint impinging upon the fan of air at asubstantial angle, the fan of air being at least as wide at the zone ofair-paint impingement as the fans of paint, whereby the air fan iseffective to atomize both fans of paint to form a spray, each fan ofpaint being in the form of a continuous sheet having a thin center weband thickened streamer portions along both edges, and projecting saidspray against a workpiece to be coated.
 35. The method of spraying paintwhich comprises the steps of projecting a flat fan of air from an airnozzle, projecting two flat fans of paint from two paint nozzles, eachfan of paint being in the form of a continuous sheet having a thincenter web and thickened streamer portions along both edges, the fans ofpaint being projected toward the fan of air from opposite sides thereofand impinging the fan of air in substantially the same area, each of thefans of paint impinging upon the fan of air at a substantial angle, thefan of air being at least as wide at the zone of air-paint impingementas the fans of paint, whereby the air fan is effective to atomize bothfans of paint to form a spray, the fan of air being non-uniform andhaving higher flow rates in the areas of impingement upon the streamerportions than in the area impinging upon the center web of the paintfans, and projecting said spray against a workpiece to be coated. 36.The method of spraying paint which comprises the steps of projecting aflat fan of air from an air nozzle, projecting two flat fans of paintfrom two paint nozzles, the fans of paint being projected toward the fanof air from the opposite sides thereof and impinging the fan of air insubstantially the saMe area, each of the fans of paint impinging uponthe fan of air at a substantial angle, the fan of air being at least aswide at the zone of air-paint impingement as the fans of paint, wherebythe air fan is effective to atomize both fans of paint to form a spray,the air flowing in a ratio of from approximately 0.2 standard cubic feetof air per minute per fluid ounce of paint per minute to approximately0.6 standard cubic feet of air per minute per fluid ounce of paint perminute, and projecting said spray against a workpiece to be coated. 37.The method of claim 33 in which the paint pressure is from approximately30 to 80 pounds per square inch.